1. Field of the Invention
The present invention relates to an electromagnetic actuator and an optical disk apparatus incorporating the same and, more particularly, to a linear actuator for driving an optical head incorporated in an optical disk apparatus for reproducing/recording information from/in an optical recording medium with a light beam.
2. Description of the Related Art
An conventional optical disk apparatus is provided with an optical system which includes a semiconductor laser for emitting a laser beam, a collimator lens for collimating the laser beam, a half mirror for splitting the collimated laser beam into two laser beams and an object lens for converging the laser beam on an optical recording medium such as an optical disk. The conventional optical disk apparatus is further provided with means for detecting a focusing state of the convergent laser beam on the optical disk to generate a focusing signal, means for detecting a tracking state of the convergent laser beam on the optical disk to generate a tracking signal, and means for retrieving an information recorded on a tracking guide formed on the optical disk to generate a retrieving signal. The objective lens is movably suspended and is moved in a focusing direction along an optical axis of the objective lens and in a tracking direction along a radial direction of the optical disk in response to the focusing and tracking signals. Thus, in the focusing and tracking states, the laser beam is focused on the optical disk and traces the tracking guide by the objective lens and information recorded on the optical disk is retrieved by the focused laser beam.
One of conventional optical disk apparatuses is disclosed in Laid Open Publication (Kokai) 1-192022, which is shown in FIGS. 1 and 2. In the optical disk apparatus shown in FIGS. 1 and 2, a lens holder 102 for supporting a objective lens 101 is suspended by leaf springs 103a, 103b which is substantially arranged in parallel and fixed on an optical block 105. A focusing coil 104 is wound around the objective lens 101 and is located in a magnetic field produced from focusing permanent magnet 110a, 110b so that the leaf spring is deformed and the objective lens 101 is moved in a focusing direction F, when the focusing coil 104 is energized The focusing permanent magnets 110a, 110b are so arranged that the magnets 110a, 110b are extended in a tracking direction T along a radial direction of an optical disk and the lens holder 102 is arranged between the focusing permanent magnets 110a, 110b.
The optical block 105 has inclined surfaces 105a, 105b at its upper and lower side and ball bearings 107a to 107h are fixed on the inclined surfaces 105a, 105b which are movably mounted on magnetic yokes 109a, 109b so that the optical block can be moved in the tracking direction along the longitudinal direction of the magnetic yokes 109a, 109b. Tracking coils 106a, 106b of a linear actuator are fixed to the optical block 105 and the magnetic yokes 109a, 109b are inserted into the tracking coils 106a, 106b, respectively so that lower sections of the tracking coils 106a, 106b are located in gaps between the magnetic yokes 109a, 109b and tracking permanent magnets 108a, 108b of the linear actuator. Thus, a tracking force is applied to the tracking coils 106a, 106b by an interaction between a current flowing through the tracking coils and a magnetic field produced from the tracking permanent magnets 108a, 108b so that the optical block 105 is moved in the tracking direction T, when the tracking coil 106a, 106b are energized.
In the conventional optical disk apparatus, a height of the apparatus along the focusing direction F can not be minimized, since the lens holder 102 for supporting the objective lens 101 and the leaf springs 103a, 103b are located above the optical block 105 and a space in which the objective lens is moved is required above the optical block 105. Further, the size of the apparatus along the focusing direction can not also be decreased, since the magnetic yokes 109a,109b are located above the tracking permanent magnet 108a, 108b. Thus, the conventional apparatus can not be designed in compact and a flat apparatus can not be realized.